For game assets is it ok to intentionally stretch UVs, or does this interfere with pixels per units?
I don't think there's anything wrong with stretching UV's from a technical perspective, it might even be desirable. 

The main thing is that from an aesthetic standpoint it looks good. I would say that as long as it looks good, and is not giving you a blurred or pixellated effect (unless that's what you want), then you should be fine.